The present invention relates to an image processing apparatus and an image processing method which store image data obtained by reading an original image by manual operation in an image memory on the basis of reading position data corresponding to the obtained image data. More particularly, the present invention relates to an image processing apparatus, an image processing method and its image reading apparatus each having a function capable of reading gray-scale image data, and its image reading apparatus.
In a conventional image reading apparatus, when an original image larger than the size of the image reading portion of a scanner is read, the apparatus has been configured such that the image is scanned a plurality of times on the original image by manually moving the scanner so that a plurality of divided images can be input. Therefore, in the conventional image reading apparatus, the plural pieces of divided image data are combined to obtain a single piece of image data, and the data is stored. The method disclosed in Japanese Laid-open Patent Application No. (Tokkai Hei) 2-159678, for example, has been known as a method of combining divided image data.
In the conventional combining method disclosed in Japanese Laid-open Patent Application No. 2-159678, a plural pieces of image data having been input dividedly are stored in an image memory. In this combining method disclosed in this Patent Application, by indicating the data in the image memory, displacements at the connection of images are confirmed, and joint end portions are designated to combine the images.
In the combining method of the conventional image reading apparatus, by combining images as described above, a composite image having few dislocation of connection is obtained in fine line pattern of characters, figures and the like.
However, in the scanner of the conventional image reading apparatus for connecting and combining images, in addition to eliminating pattern dislocations in characters, figures and the like, in case of reading by scanning a half-tone image, such as a photo image, it is necessary to prevent the generation of gray-level shifts in the image.
FIG. 33 is a view illustrating a change in gray level in the conventional image reading apparatus. The curve shown in FIG. 33 indicates a change in an image signal 100 used as an output signal obtained when an image on an original having a constant density is read at a plurality of sampling points. In other words, the curve indicates a change in gray-level data. As shown in FIG. 33, in the conventional image reading apparatus, the amount of light reflected from the original is changed by the inclination of the scanner caused during scanning. Consequently, gray-level data is changed even when the image on the original having the constant gray level is read. Since it is very difficult to maintain the inclination of the scanner at a constant angle during a manual operation in particular, gray-level data is therefore changed though in a gradual manner.
FIG. 34 is a view illustrating a method of creating a composite image C by combining images A and B having already been read. The images A and B are input by a line sensor. Even when the images are not read uniformly, gray-level differences occur at the connection portion of the composite image in the same way. When the images A and B having such gray-level differences are combined, reading positions cannot be detected accurately. Therefore, it is difficult to determine positions, on the basis of which composition is carried out.
For these reasons, in the conventional scanner, dislocations and gray-level differences are generated at the connection portion of the composite image, whereby the quality of the image is impaired significantly.